1. Field of the Invention
The present invention relates to contact masks, and more particularly to a phase shift mask having a multi-layer structure, fabricated by forming a plurality of uniformly spaced phase shift layers on a quartz substrate, capable of forming contact holes with a micro dimension smaller than the wavelength used in the light exposure procedure.
2. Description of the Prior Art
Typically, contact holes are formed using a chromium mask or phase shift mask. In the case of methods using the chromium mask to form a plurality of uniformly spaced contact holes having a micro dimension, the critical dimension of the contact holes is larger than the wavelength of exposure light. In some cases, contact holes formed using the chromium mask have a dimension larger than twice the wavelength of the exposure light. Meanwhile, the recent development of highly integrated semiconductor devices has resulted in the requirement of contact holes having a size smaller than the wavelength of the light source used in the light exposure procedure. However, it is difficult to form such contact holes because conventional chromium masks can not have a dimension smaller than the wavelength of the light source.
In order to solve the problem involved in the chromium mask, a phase shift mask has recently been proposed. Although this phase shift mask can form contact holes having a dimension smaller than the wavelength of exposure light, it can not form contact holes which are spaced at small intervals. Furthermore, this phase shift mask has a problem that its mask pattern can not be easily designed and fabricated.